As shown in FIG. 1 of the accompanying drawing, a prior art system of this kind includes one or more heat exchangers 1 fed with air from a stage of a compressor of a propulsion jet engine of the aircraft, for example. The air is cooled by external air flowing through the heat exchanger from an air inlet 2 on the outer skin 3 of the aircraft, The external air passes through a pipe 4 and is returned to the exterior via an outlet 5 of the pipe, also on the fuselage 3.
The air cooled in the heat exchangers 1 is fed to various ancillary units, turbines, water separator, etc., and is blown into the cabin 6 of the aircraft, for example through a cool air inlet 7 in a wall 8 of the cabin.
A cabin air outlet 9 also passes through the cabin wall and is equipped with a pressurization valve 10 by means of which the air pressure in the cabin is regulated to a predetermined set point value, usually of the order of 700 to 900 mb at cruising altitude.
A system of the above kind is known in the art, in particular from French patent application No. 99 14147 filed 10 Nov. 1999 by the applicant, which may be referred to for further details concerning the arrangement of the heat exchangers and the associated equipment.
One essential problem to be solved in systems of the above type is that of ventilating the heat exchangers, i.e. circulating external air in the pipe 4. A fan 11 In the pipe 4 downstream of the heat exchangers and driven by an electric motor 12 or a turbine can be used for this, as shown in FIG. 1.
This solution can be envisaged in conjunction with a static air inlet 2, as shown in FIG. 1, which is substantially tangential to the trajectory of the aircraft, or a “dynamic” air inlet, like that of the system described in the patent application previously cited, which is open toward the front of the aircraft so that external air is scooped into the air inlet.
Systems with dynamic air inlets have the disadvantage of operating only if the aircraft is travelling at sufficient speed. It is therefore essential to equip them with a fan for circulating air in the pipe when the aircraft is travelling at a low speed or is on the ground. A dynamic air inlet also increases the drag on the aircraft and necessitates the provision of de-icing means. The shape of the air inlet is very complex and requires many costly fabrication hours.
Systems with a static air inlet, like that described above with reference to FIG. 1, have the disadvantage of being inadequate at high altitudes if the fan is designed to operate with air of normal density at low altitude or on the ground. Because the density of the air at high altitudes is very low, the fan may then not provide a sufficient flow of air for the air that is to be blown into the cabinet to be cooled effectively. Consideration might then be given to equipping the system with two fans respectively designed to ventilate the heat exchangers at high altitudes and at low altitudes, but this solution is obviously costly.
Thought might also be given to ventilating the heat exchangers by means of an ejector fed with air taken from an air circuit between a source (propulsion or auxiliary engine) and the cabin, but this solution increases the energy consumed by the source and is therefore not economical either.
Thus an object of the invention is to provide a system for supplying an aircraft with cool air that is free of the drawbacks of the prior art systems previously mentioned and which in particular is economical in terms of energy consumption and manufacturing cost.